A buried resistor is a standard element in bi-complementary metal oxide semiconductor (biCMOS) technologies. A typical buried resistor consists, for example, of an n+ doped region in a p-type substrate (or p-well) or a p+ doped region in an n-type substrate (or n-well).
Another type of resistor used in certain integrated circuit (IC) technologies is polysilicon on a thick oxide structure that provides lower capacitance to the substrate. These resistors, which are sometimes referred to as polySi resistors, can also be built over an n-well or p-well, for example. However, polySi resistors are not generally compatible with CMOS technologies which do not offer a blocked silicidation process feature. Furthermore, buried resistors have a much greater heat dissipation capability and are less expensive to manufacture, thus generally more desirable for many applications.
Although buried resistors are widely used in biCMOS circuit designs, such resistors typically carry low currents (on the order of about 1 mA-μm or less) which greatly limits their use. Moreover, prior art buried resistors have a sheet resistance tolerance that is greater than 10% and, as such, no precision buried resistor design is presently available.
In view of the above drawbacks with prior art buried resistors, there is a need for providing a buried resistor that is capable of carrying high currents (on the order of about 1 mA-μm or greater) and which has a sheet resistance tolerance of less than 10%. That is, a precision buried resistor is needed that has an improved sheet resistance control.